Dynamics of Membrane Tethers Reveal Novel Aspects of Cytoskeleton-Membrane Interactions in Axons

Mechanical properties of cell membranes are known to be significantly influenced by the underlying cortical cytoskeleton. The technique of pulling membrane tethers from cells is one of the most effective ways of studying the membrane mechanics and the membrane-cortex interaction. In this article, we show that axon membranes make an interesting system to explore as they exhibit both free membrane-like behavior where the tether-membrane junction is movable on the surface of the axons (unlike many other cell membranes) as well as cell-like behavior where there are transient and spontaneous eruptions in the tether force that vanish when F-actin is depolymerized. We analyze the passive and spontaneous responses of axonal membrane tethers and propose theoretical models to explain the observed behavior.     

Impaired Bone Homeostasis in Amyotrophic Lateral Sclerosis Mice with Muscle Atrophy

There is an intimate relationship between muscle and bone throughout life. However, how alterations in muscle functions in disease impact bone homeostasis is poorly understood. Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by progressive muscle atrophy. In this study we analyzed the effects of ALS on bone using the well established G93A transgenic mouse model, which harbors an ALS-causing mutation in the gene encoding superoxide dismutase 1. We found that 4-month-old G93A mice with severe muscle atrophy had dramatically reduced trabecular and cortical bone mass compared with their sex-matched wild type (WT) control littermates. Mechanically, we found that multiple osteoblast properties, such as the formation of osteoprogenitors, activation of Akt and Erk1/2 pathways, and osteoblast differentiation capacity, were severely impaired in primary cultures and bones from G93A relative to WT mice; this could contribute to reduced bone formation in the mutant mice. Conversely, osteoclast formation and bone resorption were strikingly enhanced in primary bone marrow cultures and bones of G93A mice compared with WT mice. Furthermore, sclerostin and RANKL expression in osteocytes embedded in the bone matrix were greatly up-regulated, and β-catenin was down-regulated in osteoblasts from G93A mice when compared with those of WT mice. Interestingly, calvarial bone that does not load and long bones from 2-month-old G93A mice without muscle atrophy displayed no detectable changes in parameters for osteoblast and osteoclast functions. Thus, for the first time to our knowledge, we have demonstrated that ALS causes abnormal bone remodeling and defined the underlying molecular and cellular mechanisms.     

Mutational approach for N2-fixing and P-solubilizing mutant strains of Klebsiella pneumoniae RSN19 by microwave mutagenesis

Nitrogen (N) fixing Klebsiella pneumoniae RSN19 has high inorganic phosphorus (P) solubilizing capability, but its N₂-fixing capability is limited. In order to acquire a P-solubilizing mutant strain with high efficiency N-fixing capability, different microwave irradiation intensities and durations were tested on RSN19 in an attempt to produce mutants with improved N₂-fixation and P-solubilization capabilities. The effect of microwave irradiation power and time were studied and the microwave mutagenesis parameters were optimized. Nitrogenase activity was tested on the mutant strains by acetylene reduction method; and their P-solubilizing capability and genetic stability were determined. The results indicated that the best conditions for microwave mutagenesis that produced better performed mutant strains were 250W, 36 s. Under these conditions a maximum positive mutation rate of 1.66% was obtained, resulting in five genetically stable strains with promoted nitrogenase activity which was designated as RSM-219, RSM-206, RSM-224, RSM-225 and RSM-275. Subculture tests showed that RSM-219 and RSM-206 were genetically stable mutant strains with higher nitrogenase activity and phosphate solubilizing capabilities than the original strain. Both RSM-219 and RSM-206 performed better than the original strain under N-free conditions when supplied with calcium phosphate only, and produced greater increases in the biomass of alfalfa seedlings.     

Stable and orally bio-available pro-drugs of CPS11

Stable and orally bio-available pro-drugs of CPS11 were synthesized. They are active on human umbilical vein endothelial cell proliferation assay and tube formation assay. The therapeutic efficacy and safety of 4 as a single agent or combined with Taxol in the treatment of MX-1 human breast cancer xenograft were evaluated. Compound 4 as a single agent failed to produce an anti-tumor activity, while it significantly enhanced antitumor potency of Taxol.     

噬菌体展示HIV-1 Tat38-61碱性区51和55位随机突变体文库的构建

为了构建噬菌体展示Tat38-61(51N/55N) 碱性区突变体文库,进一步研究HIV-1 Tat38-61表位的分子进化筛选,采用含随机核苷酸序列的引物,通过Overlap PCR的方法获得51和55位氨基酸随机突变的全长Tat编码序列,再以此为模板PCR扩增出两端含有Xba I识别序列的Tat38-61突变体片段HIV-1 Tat38-61(51N/55N),克隆至噬菌体展示载体pCANTAB5S上,转化大肠杆菌TG1,经M13K07辅助噬菌体拯救,构建噬菌体展示Tat38-61(51N/55N) 碱性区突变体文库。结果显示文库的库容量为5.0×106,滴度为2.65×1012 TU/mL,阳性克隆率为56.50％;序列分析显示文库中51、55位核苷酸与氨基酸均呈随机性分布,达到了对文库进行分子进化筛选的要求,为获得可用作疫苗候选物的新型Tat突变体奠定基础。     

Identification of a truncated form of methionine sulfoxide reductase a expressed in mouse embryonic stem cells

Background  

Methionine Sulfoxide Reductase A (MsrA), an enzyme in the Msr gene family, is important in the cellular anti-oxidative stress defense mechanism. It acts by reducing the oxidized methionine sulfoxide in proteins back to sulfide and by reducing the cellular level of reactive oxygen species. MsrA, the only enzyme in the Msr gene family that can reduce the S-form epimers of methionine sulfoxide, has been located in different cellular compartments including mitochondria, cytosol and nuclei of various cell lines.     

微滴培养技术的新应用

微滴培养技术在卵母细胞培养和胚胎早期发育研究中有广泛的应用.近期研究发现这项技术又有新的应用范围.有科学家发现将该技术应用于胚胎干细胞可以实现高效传代,在精原干细胞培养和精子发生相关过程的研究方面也可取得很好效果,同时,对早期人类胚胎干细胞的分离过程的监控和对精原干细胞生长过程的观察也相对容易.这些研究结果显示,微滴培养技术在这些新领域的研究与常规培养方法相比具有独特的优势.回顾微滴培养技术的主要发展过程,重点探讨微滴培养技术的最新应用及其优点.